1. Field of the Invention
The present invention relates to a method for unlocking a subscriber identity module (SIM) card lock, more particularly to a method, which is implemented through unstructured supplementary system data (USSD) and over-the-air (OTA) mechanisms, for unlocking a SIM card lock.
2. Description of the Related Art
Contracts are usually made with telecommunications service providers when mobile terminals, such as mobile phones, are sold. Aside from storing phone number and contract content in a SIM card provided thereby, the telecommunications service providers require mobile terminal manufacturers to perform SIM card locking upon mobile terminals such that the mobile terminals are operable only when correct SIM cards are inserted thereinto. For example, a mobile terminal may be locked for only accepting a SIM card having a specific International Mobile Subscriber Identity (IMSI) code. An IMSI code is usually presented as a 15 digit code, and is composed of a Mobile Country Code (MCC), a Mobile Network Code (MNC), and a Mobile Station Identification Number (MSIN). The 3rd Generation Partnership Project (3GPP) stipulates five ways to execute SIM card locking.
A simple SIM card lock may be unlocked by a subscriber entering an unlocking password supplied by the mobile terminal manufacturer to the telecommunications service provider. However, for current advanced mobile terminals, they must be connected to a computer and use a specific program to load the unlocking password for unlocking.
The aforesaid SIM card lock mechanism constrains usage of mobile terminals. For example, when a user is in an area not supported by the contracted telecommunications service provider, the user may not use local telecommunications services by inserting a SIM card purchased locally into the mobile terminal.
Even when the contract has expired, the telecommunications service provider may not unlock the SIM card lock actively, since the telecommunications service provider always desires subscribers to continue using telecommunications services provided thereby. Moreover, even though the telecommunications service provider is capable of unlocking the SIM card lock, such as by adopting unlocking techniques disclosed in U.S. Pat. Nos. 6,321,079 and 7,689,204, the subscribers are generally not allowed to unlock a SIM card lock with relative ease. Therefore, a method for legitimately unlocking a SIM card lock which is acceptable to the telecommunications service providers and which facilitates unlocking of SIM card locks by the subscribers is being sought.